Process for the manufacture of photographic material containing oxidized polysaccharides



United States Patent ()fitice 3,368,891 Patented Feb. 13, 1968 3,368,891 PROCESS FOR THE MANUFACTURE OF PHOTO- GRAPHIC MATERIAL CONTAINING OXIDIZED POLYSA'CCHARIDES Jean Lucien Laenen, Edegem, Belgium, assignor to Gevaert Photo-Producten N.V., Mortsel-Autwerp, Belgium, 2 company of Belgium No Drawing. Filed Mar. 10, 1964, Ser. No. 350,686 Claims priority, application Belgium, Mar. 12, 1963,

Claims. (Cl. 96-1) ABSTRACT OF THE DISCLOURE In the manufacture of pigmented photographic paper, the pigment layer contains as a binding agent an alkali or ammonium salt of casein or soybean protein and is hardened by means of a polysaccharide which has at least some, preferably 50-100%, of its secondary alcohol groups converted into aldehyde groups, or water-soluble derivatives of such polysaccharides.

Photographic paper is generally composed of the following layers.

(1) A paper support,

(2) A so-called pigment layer, usually coated from a dispersion of a pigment such as barium sulfate, titanium dioxide, etc., in a hydrophilic or hydrophobic colloid as binding agent,

(3) The actual image-layer which may be a light-sensitive layer or a layer containing development nuclei wherein an image can be formed according to the silver complex diffusion transfer process.

In general, all pigments applied in the paper industry for sized paper may be used for the pigment layer with the proviso, however, that said pigments do not adversely affect the light-sensitive layer or the development nuclei.

It is evident that in addition to these three principal layers the photographic paper may still comprise other layers, e.g., a subbing layer improving the adhesion of the light-sensitive layer to the pigment layer containing a hydrophobic binding agent, a filter layer, etc.

By the term light-sensitive layer used in the description and the claims is meant not only light-sensitive layers on the basis of silver halides or other light-sensitive compounds but also layers containing photoconductive pigments for use in electrophotography.

The properties of the photographic material are dependent on the quality of the light-sensitive layer or of the layer containing development nuclei, of the pigment layer and of the paper support. In this connection there may be mentioned that the physical irregularities of the surface of the pigment layer are reproduced in the light-sensitive layer and after processing said irregular ities, often enlarged, can be observed in the light-sensitive layer since they prevent to obtain a light-sensitive layer of uniform thickness. Therefore the surface of the pigment layer should be as uniform as possible in view of obtaining a product of maximum quality.

As hydrophilic binding agent for the pigment layer is generally used gelatin in the presence of formaldehyde. For preventing the aqueous gelatin solution from penetrating too strongly into the paper support the gelatin is gelled by cooling which also facilitates the further treatment of the sized paper support. The use of gelatin hardened by means of formaldehyde, however, entails some disadvantages on the pigment layer among others:

(1) A very difficult dosing of the hardener (owing to volatility of formaldehyde).

(2) An undesired hardening of additional layers (owing to diffusion of the hardener).

It has now been found that these disadvantages are waived by using as binding agent for the pigment layer an alkali or ammonium salt of casein or of soybean protein to which an oxidized polysaccharide or a watersoluble derivative of an oxidized polysaccharide has been added which is alkaline medium has an optimum hardening action.

The process according to the invention for the manufacture of photographic material comprising a paper support and a pigment layer applied thereto, is characterized in that said pigment layer is formed from a suspension of a pigment in an aqueous solution of an alkali or ammonium salt of casein or of soybean protein to which anaqueous solution of an oxidized polysaccharide or of a water-soluble derivative of an oxidized polysaccharide has been added.

In the further description the term .oxidized polysacharides stands for oxidized polysaccharides as well as for their water-soluble derivatives.

The use of an alkali or ammonium salt of casein' or of soybean protein mixed with an amount of oxidized polysaccharide as binder for the photographically inert pigment olfers more particularly the following advantages:

(1) An axact dosage of the amount of hardener added,

(2) The possibility to disperse a larger amount of pigment in the binding agent, and

(3) After coating a faster coagulation of the binding agent under the influence of the oxidized polysaccharide which exercises a hardening action upon the alkali or ammonium salt of casein or of soybean protein whereby less binder solution penetrates into the paper support, a smoother surface is obtained and in consequence thereof a higher gloss is'achieved.

The oxidized polysaccharides are obtained by treating polysaccharides With an aqueous solution of a periodate such an sodium periodate. By this treatment the secondary alcohol groups of the pyranose units of the polysaccharide are at least partially converted into aldehyde groups. Best results are obtained when from 50 to of the secondary alcohol groups are converted into aldehyde groups.

Polysaccharides which are especially suited for being oxidized and used according to the present invention are; starch, watersolu ble polysaccharides such as carboxymethyl cellulose, water-soluble methyl cellulose, watersoluble derivatives of starch, polysaccharides the dialdehyde derivatives of which are water-soluble such as amylopectine, further alginic acid and salts thereof, pectic acid and salt thereof, gum arabic and xylan. The hardening action of the oxidized polysaccharide upon the alkali or ammonium salt of casein or of soybean protein increases with the concentration of oxidized polysaccharide and with the number of aldehyde groups present in its macromolecule. The amount 'of oxidized polysaccharide added depends on the hardening degree. desired; it lies, however, generally between 0.5 and 50% by weight and preferably between 1 and 7% by weight relative to the amount of dry alkali or ammonium salt of casein or of soybean protein. The amount of alkali or ammonium salt itself lies between 5 and 50%, preferably between 6 and 10% by weight relative to the amount of dry pigment.

As photographically inert pigment barium sulphate is preferably used although titanium oxide and other inert pigments are also suited.

The suspension of pigment in alkali or ammonium salt 0 of casein or of soybean protein, together with oxidized polysaccharide is coated onto the paper web in such a way that after uniformly spreading out and drying from 10 to 3 60 g. per sq. m. of dry substance is present. Occasionally the amount of dry substance may fall outside these limits. The pigment suspension may be applied as a layer to the paper support by means of an air knife, brushes or any other spreading machine.

The pigment layer according to the invention may successfully be coated upon paper supports destined for the manufacture of photographic paper. Onto said pigment layer one or more light-sensitive photographic layers may be coated, for instance one or more light-sensitive gelatino silver halide emulsion layers. The pigment layer described above may also be successfully applied in photographic papers destined for electrophotographic applications. In that case the pigment layer or a layer applied thereto should contain photoconductive substances of use in electrophotography. The pigment layer may further be applied in non-light-sensitive photographic paper, for instance in the positive image-receiving material destined for producing images according to the silver complex diffusion transfer process.

The following examples illustrate the invention.

Example I To a paper web a pigment layer is applied from the following composition according to known methods:

Water cc- 460 Casein g 43 Dialdehyde starch g 1.6 20% aqueous ammonia cc 25 56% aqueous suspension of barium sulphate g 1000 To a paper web a pigment layer is applied from the following composition according to known methods:

Water cc 200 Casein g 50 Dialdehyde amylopectin g 5 aqueous ammonia cc 56% aqueous suspension of barium sulphate g 1000 This compensation is applied in 3 or 4 times to the paper web so that a layer of 60 g. per sq. m. is obtained.

The dialdehyde amylopectin was obtained by oxidation into aldehyde groups of 55% of the secondary alcohol groups of the amylopectin.

After drying, the known photographic layers are coated.

Example 3 To a paper web a pigment layer is applied from the following composition according to known methods;

4 Water cc 420 Soybean protein g Dialdehyde starch g 30 40% aqueous suspension of titanium oxide g 1680 20% aqueous ammonia cc 27 This composition is applied pro rata of 10 g. per sq. m.

The dialdehyde starch was obtained by oxidation of 78% of the secondary alcohol groups of starch.

The smoothness of the surface and the hardening are favourably influenced by calendering at elevated temperatures for instance at 60 C.

After drying, the known photographic layers are coated.

I claim:

1. In a process for manufacturing photographic material comprising a paper support and a pigment layer carried on said support, the improvement which comprises forming said pigment layer from a suspension of a pigment in an aqueous solution of an alkali or ammonium salt of casein or soybean protein, said aqueous solution having incorporated therein a polysaccharide having the secondary alcohol groups thereof at least partially converted into aldehyde groups or a water-soluble derivative of said aldehyde-modified polysaccharide.

2. The process of claim 1 wherein said aldehyde-modified polysaccharides or watersoluble derivative thereof is incorporated in the amount of 05-50% by weight of the casein or soybean protein salt.

3. The process of claim 1 wherein said aldehyde-modified polysaccharide is dialdehyde starch.

4. The process of claim 1 wherein said aldehyde-modified polysaccharide is dialdehyde amylopectin.

5. The process of claim 1 wherein 50-100% of the secondary alcohol groups of said polysaccharides are converted into aldehyde groups.

6. The process of claim 1 wherein said adlehyde-modified polysaccharide or water-soluble derivative thereof is added to said pigment solution in the form of an aqueous solution.

7. Photographic material obtained according to claim 1, wherein at least one light-sensitive layer as defined hereinbefore is applied to the pigment layer.

8. Photographic material according to claim 1, wherein at least one light-sensitive silver halide emulsion layer is applied to the pigment layer.

9. Photographic material obtained according to claim 1 for use in the silver complex diffusion transfer process wherein a layer selected from said pigment layer and a layer applied thereto contains development nuclei.

10. Photographic material obtained according to claim 1 for use in electrophotography wherein a layer selected from said pigment layer and a layer applied thereto contains photoconductive pigments.

References Cited FOREIGN PATENTS 891,221 3/1962 Great Britain.

TORCHIN, Primary Examiner. 

